Calender arrangement and a deflection controlled roll and method of operating them

ABSTRACT

A calender arrangement includes end rolls that are in the form of deflection controlled rolls having an internal stroke. One of the end rolls comprises at least one stop element that is in the form of a hydraulic positioned hydrostatic element which, together with the internal wall of the roll sleeve, defines a gap. When a constant throughput of hydraulic medium is fed in, an equilibrium of forces is produced, at which equilibrium the roll sleeve is positioned. The pressure built up in the process is a measure of the positioning forces. Small departures from the target position are permitted without control intervention.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is,a continuation-in-part of application Ser. No.09/297,394, filed on Jun. 10, 1999 (now abandoned) the full disclosureof which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a calender arrangement for treating a productweb, especially a paper web. The invention relates also to a deflectioncontrolled roll having internal roll sleeve stroke and to a method offixing an operating position of such a deflection controlled roll whenit is being used as an end roll in a stack of rolls of a calenderarrangement.

From DE 30 04 913 C2 it is known to use a deflection controlled rollboth for the upper and lower end roll of a stack of rolls in a calender,in which deflection controlled roll the roll sleeve is supported byhydrostatic sleeve support elements on a roll axle that is securedagainst rotation in lateral bearings, and is movable vertically relativeto the roll axle, that is to say it is provided with an internal rollsleeve stroke. The intermediate rolls of the stack of rolls are alsoconfigured so as to be movable vertically. Since the vertical positionof the entire stack of rolls must be preset in some manner duringoperation, stops are provided for that purpose. The roll axle of eachdeflection controlled roll accordingly passes through a verticalelongate hole in a bearing side support of the roll sleeve in such amanner that the roll sleeve is movable vertically relative to the rollaxle within the range of the elongate hole. Under the influence of thesleeve and loading arrangement, the roll sleeve of one end roll moves inthe vertical direction until at both its ends it comes to rest with thestop of the elongate hole against a counterstop associated with the rollaxle and thus reaches a defined preset position (operating position) ofthe roll sleeve and therefore of the entire stack of rolls, and is heldin that operating position during operation. A disadvantage therein isthat during operation of the calender unavoidable vibrations of themachine parts. intensified by a rigid mechanical stop, are transferredto the roll sleeve and to the entire roll system and may result in animpairment of the product web to be treated. It is a furtherdisadvantage that only one position, namely the outermost eccentricposition of the roll sleeve stroke, which is provided by a rigidmechanical stop, serves to preset the operating position. The fact thatthe roll sleeve is supported in the stop also means that the line loadprofile has restricted (limited) controllability.

From DE 34 16 210 C2 there is known a roll press having an end roll, inwhich the roll sleeve is mounted near its end on the associated rollaxle. Arranged in the region of the bearings are force sensors, theoutput signals of which so influence a controller for the supportingforces of the hydrostatic support elements acting upon an internalcircumference of the roll sleeve that the detected forces are minimized,that is to say, as small forces as possible are transferred to the rollsleeve by way of the bearings. In the development of that arrangementaccording to DE 39 09 911 C1, hydraulic force sensors are used. Adisadvantage thereof is that such an end roll without internal rollsleeve stroke relative to the roll axle cannot be used as a self-loadingdeflection controlled roll that enables substantially more precisesetting and control of the loading forces, that is to say of the lineload profile. A further disadvantage is the complexity of the controlsystem and the limitation to only one vertical operating position of theroll sleeve.

The same disadvantages affect the roll arrangement according to DE 29 43644 C2 in which the relative heights of the roll axle and roll sleeve ofan end roll are so controlled that the roll axle adopts an approximatelymiddle position in the roll sleeve.

From DE 39 18 989 C1 it is known, in a deflection controlled roll, forthe vertical extension movement of hydrostatic support elements thatbear against the roll axle so as to be vertically displaceable and thatact by at least one open hydrostatic bearing pocket against an internalcircumference of the roll sleeve to be limited by means of stops. When astop is reached, the support element is secured mechanically and cannotextend further. This results in a specific positioning of the rollsleeve relative to the roll axle. A disadvantage thereof is that thepositioning is effected by the actual transmission of forces for settingthe line load and, consequently, alters with the latter, resulting inchanges in reference position in dependence upon changes in thetransmission of forces.

Finally, from DE 42 03 497 A1 there is known a compensating roll for thepressure treatment of product webs, consisting of a stationary roll coresurrounded by a rotating roll sleeve which is supported on the roll axleand is vertically displaceable by means of hydraulic support elementslying next to one another, the support elements being arranged on twodiametrical lines of the envelope of the roll axle. As a result of thehydraulic support elements' being acted upon by pressure medium atspecific pressure values, the resulting forces co-operate and enable thelongitudinal and sectional deformation of the roll sleeve. Adisadvantage thereof is that such a compensating roll is configuredwithout an internal roll sleeve stroke, so that the above-mentioneddisadvantages occur in this case also.

The problem underlying the invention is therefore so to configure acalender arrangement so that one and the same device enables positioningof the roll sleeve of a self-loading end roll having an internal sleevestroke, which carries intermediate rolls, held so as to be displaceablevertically, of a stack of rolls and is thus able to set a desired lineload profile in the roll nip precisely, and enables detection andcontrol of the forces acting in the positioning region.

A further problem is to provide a deflection controlled roll whichenables positioning of the roll sleeve relative to the roll axle in anoperating position without substantial additional expenditure.

SUMMARY OF THE INVENTION

A calender arrangement is accordingly provided in which an end roll isconfigured as a deflection controlled roll having internal stroke and isarranged to be fitted with the device for positioning the roll sleeverelative to the roll axle. In the operating state of the calender, theroll sleeve is held in an operating position by means of the positioningdevice. The roll sleeve carries displaceable intermediate rolls of astack of rolls. Mounting the roll sleeve on support elements and on atleast one stop element enables extremely precise setting and control ofa line load profile in the entire roll nip.

The opposite end roll can also be configured as a deflection controlledroll having internal stroke and which can be equipped in the same manneras the one end roll.

The term “pseudo-stop” is intended to show that the position of the rollsleeve relative to the axle is not determined by mechanical componentslying next to one another, but that the hydraulic medium film isinterposed in the through gap between the stop element and the rollsleeve. The height of the through gap depends upon the pressure of thehydraulic medium that is fed in, which is a measure of the positioningforces.

A deflection controlled roll having internal roll sleeve stroke isprovided that enables positioning of the roll sleeve by hydraulic means.The hydraulic stopper operates by virtue of the limited element stroke,which secures it on the roll axle with a selectable stroke, in themanner of an overflow valve, and thus stops and holds the roll sleeve ina selectable operating position. Within the range of the internalstroke, the deflection controlled roll can accordingly be displaced to apredeterminable position and fixed there.

If the hydrostatic bearing pocket of a stopper that has been pushed tothe maximum stroke is supplied with a constant oil or pressure mediumflow, a pressure can build up in that bearing pocket when the internalcircumference of the roll sleeve draws closer to the bearing pocket. Thepressure can build up to a predeterminable target value at which thebearing pocket rests against the internal circumference of the rollsleeve with a seal gap of a specific gap height resulting from the flowthrough the gap corresponding to the target pressure value. If thatspecific gap height is reduced as a result of external disturbingforces, the pressure in the bearing pocket rises and produces anopposite force. If the specific gap height is increased as a result ofexternal disturbing forces, the pressure in the bearing pocket falls, asa result of which an opposite force is likewise produced.

Such a hydraulically positioned hydrostatic stopper is not involved inthe actual transmission of forces. A target oil pressure can thus be soset to obtain a specific rigidity of fixing, that is to say the systemis, on the one hand, not too rigid but, on the other hand, is not tooyielding. The damping of oscillation can thus be optimized.

The hydraulically positioned hydrostatic stopper in the form of apiston/cylinder unit can also be provided with a piston diameter that isdifferent from that of the actual load transmission elements, that is tosay the support elements, in order to be able to influence thesupporting forces of those elements further. The same applies also tothe sealing edge widths of the hydraulically hydrostatic stoppers.

Rises and falls in pressure in the bearing pocket of a stopper areadditionally indicators of undesired radial roll sleeve displacements.The changes in pressure value in the bearing pockets can therefore bemeasured and used as control signals for regulating the supportingforces of the support elements. If, for example, the pressure in thebearing pocket of a stopper rises above the target pressure value as aresult of direct or indirect vertical roll sleeve displacements, thatrise in pressure can, when a predeterminable maximum pressure value hasbeen reached, trigger a control signal which can be sent to a controllerfor the support elements which alters the supporting forces in such amanner that the target pressure value is restored. If the pressure inthe bearing pocket falls below the target value, a control signal canlikewise be sent to the controller for the support elements when apredeterminable minimum pressure value has been reached, and thecontroller can alter the supporting forces in such a manner that thetarget pressure value is restored. The roll sleeve is thus hydraulicallyclamped at the predetermined operating position and held there.

The effective range of the securing can also be determined by way of atarget pressure in a bearing pocket of the stopper. The effective rangeis firstly the difference between the target pressure and a maximumpressure in the bearing pocket, which can be firmly predetermined by wayof a pressure limiting valve in a pressure fluid supply line, andsecondly the difference between the target pressure and the minimumpressure in the bearing pocket, which can be determined by means of theselected target pressure. Forces are thus controlled. In that manner,the roll and the roll sleeve can be protected from being destroyed. Thetarget pressure of a stopper can be selected as desired, since it can betaken into account as a value that can be firmly set in the profilecalculations, its value not being the result of the oil pressureoptimization in the support elements.

It is also advantageous if at least two stoppers are arranged in such amanner that they lie approximately at the quarter points of the roll,because there they produce the smallest profile errors, considering theintermediately supported rolls, when there are departures from a targetpressure.

It is also advantageous for the stoppers for positioning the roll sleeveto be incorporated additionally into the roll as independentbackward-facing elements having independent pressure fluid supplies.

It is also advantageous to incorporate the deflection controlled rollaccording to the invention into a calender in such a manner that thestoppers are arranged on the backward-facing side of the roll. In theevent of pressure changes, which are admittedly small in troublefreenormal operation, local departures from the line loading can thus beminimized.

Further developments and advantages of the invention can be found in thefollowing description and in the dependent claims.

The invention will be explained hereinafter in greater detail withreference to the embodiments shown in the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section of a deflection controlled roll havingstoppers according to a first embodiment;

FIG. 2 is an axial section through a stopper according to FIG. 1 andshows also the hydraulic medium supply line;

FIG. 3 is a section according to line 3—3 in FIG. 2;

FIG. 4 is a pressure/nip width graph;

FIGS. 5a-5 c are diagrammatic side views of three calender arrangementsaccording to the invention having deflection controlled rolls accordingto FIG. 1 where the stack planes are vertical, oblique, and horizontal,respectively;

FIG. 6 shows a modified stopper;

FIG. 7 is a longitudinal section of a deflection controlled roll havingstoppers according to a second embodiment;

FIG. 8 is an axial section through a pair of stoppers according to FIG.7;

FIG. 9 is a longitudinal section of a deflection controlled roll havingstoppers according to a third embodiment;

FIG. 10 is an axial section through a stopper/support element pairaccording to FIG. 9;

FIG. 11 is a longitudinal section through a deflection controlled rollhaving stoppers according to a fourth embodiment;

FIG. 12 is an axial section through a pair of stoppers according to FIG.11;

FIG. 13 shows a differently modified stopper;

FIGS. 14a and 14 b are diagrammatic cross-sections of a lower end rolland an intermediate roll arranged above it of a calender arrangementaccording to the invention, to illustrate the design principle andworking principle of a calender.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first embodiment of a self-loading deflection controlledroll that can be used, for example, as a lower end roll 62 of a calenderarrangement, which deflection controlled roll has a roll axle 10, theprojecting ends of which can be secured against rotation in a calenderframe 12 (merely indicated) (see FIG. 5). Mounted to rotate about theroll axle 10 is a roll sleeve 14, which can be displaced radiallyrelative to the roll axle 10 by means of at least one guide insert, forexample side supports 11, and which is supported on the roll axle 10 bymeans of radially displaceable hydrostatic support elements 16. The rollaxle 10 is spaced on all sides from the internal circumference 13 of theroll sleeve 14 so that the roll sleeve 14 can be displaced verticallyrelative to the roll axle 10. The deflection controlled roll thus has aso-called internal stroke. The support elements 16 are orientedvertically upwards and carry the roll sleeve 14 in the embodimentaccording to FIG. 5a where the rolls are arranged in a vertical stackplane. Alternatively, the rolls may be arranged in an oblique stackplane (FIG. 5b) or in a horizontal plane (FIG. 5c).

The support elements 16 are in this case in the form of hydrostatic sealelements, as described, for example, in DE 3820974 C3 or DE 39 18 989C1. In those specifications, support elements 16 act against theinternal circumference 13 of the roll sleeve 14, which support elementsare in the form of sealing members 15 that delimit hydrostatic bearingpockets 17, to which hydraulic pressure fluid can be supplied by way offirst lines 18. The sealing members 15 are so guided as to bedisplaceable vertically in blind bores 19 in the roll axle 10, theirextensibility being provided by way of a hydraulic piston/cylinder unit(not shown further) having associated pressure medium supply.Alternative developments of the support elements 16, as described, forexample, in DE 31 19 387 C2, can also be used.

A plurality of such support elements 16, in this case, for example, 8,are arranged in a series extending along the length of the roll axle 10.

At least one stopper or stop elements 20 is/are provided on the rollaxle 10, offset by 180° in the circumferential direction, that is to sayon a diametrical or opposite line relative to the series arrangement ofthe support elements 16. According to the embodiment shown in FIG. 1,two stoppers 20 are preferably provided spaced from one another. Thestoppers 20 are preferably hydraulically positioned hydrostatic stoppers20 in the form of hydrostatic support elements having a securing stop,as shown in detail in FIGS. 2 and 3. According to FIG. 1, the stoppers20 act, for example, in the downward direction whereas the supportelements 16 act in the upward direction.

According to FIGS. 2 and 3, each stopper 20 comprises a sealing memberor plunger 22 having a piston-like cylindrical body which is guided soas to slide in a bore 24 in the roll axle 10. An operating positionshown in FIG. 2, in which the sealing member 22 is in a selectableextension position, is determined by stops. The stops are formed byheaded bolts 28 which, at the same time, secure the sealing member 22against twisting and which are attached into the roll axle 10. Heads 26of the headed bolts 28 determine a clearly defined maximum extensionposition of the sealing member 22 and thus a clearly defined positionrelative to the roll axle 10. The heads 26 form the securing stop. Thestopper 20 thus has a limited element stroke which can be selectablypreset and constitutes a limitation to the stroke. The sealing member 22is held in its operating position by hydraulic medium fed into a blindbore 38 by way of a line 37.

Two channels or passages 30 pass through the sealing member 22 and aresupplied with hydraulic medium. The sealing member 22 makes contact atan end face or contact surface 32 that is matched to the internalcircumference 13 of the roll sleeve 14. There are formed in the end face32 at least one, preferably more, flat bearing pockets 23 which take upa substantial portion of the end face 32, so that rim-forming webs areall that remain thereof. The end face 32 together with the roll sleeve14 delimits a gap 34 through which the hydraulic medium supplied via thechannels 30 can emerge.

Hydraulic medium is supplied to the channels 30 by way of an inlet 36formed in the roll axle 10. A supply line 40 extends through the rollaxle 10 to a pump 42, driven by a motor 44, to a supply container 41.

The hydrostatic bearing pockets 23 of a stopper 20 are supplied with aconstant oil or pressure medium volumetric flow and initially the flowis virtually without pressure. When the internal circumference 13 of theroll sleeve 14 draws closer to the bearing faces 32 of the stopper 20,as a result of which the seal gap 34 of the stopper 20 is produced,pressure corresponding to the constant volumetric flow builds up in thehydrostatic pockets 23 until a predeterminable target value is reached,and a gap height S (which is, in the 4, range, for example, about 50˜i)is produced according to the corresponding gap flow. The contactpressure required for the hydraulically positioned hydrostatic stopper20 is built up through the separate pressure oil line 37.

If, as a result of an inequality, caused by external disturbing forcesacting upon the roll sleeve 14, the stopper 20 is pressed upwardsthrough a slight stroke movement within the range of the seal gap 34,that is to say in the a range, the pressure in the stopper 20 rises andproduces an opposite force which continues to rise until equilibrium isrestored. The stopper 20 is, as a consequence, a position indicatorresponding by means of pressure value changes in the bearing pocket 23to vertical roll sleeve displacements and producing an opposite force.

If the opposite force is unable to restore the equilibrium of the forcesin the support and loading system and the pressure in the stopper 20continues to rise to a predeterminable maximum pressure value, that risein pressure triggers (by means of the transducer 50) a control signalwhich is sent to a controller 52 for the support elements 16 which soalters the supporting forces that a state of equilibrium in the regionof the target pressure value is restored.

If, on the other hand, as a result of an inequality, the roll sleeve 14moves away from the stopper 20 within the range of the seal gap 34, thepressure in the stopper 20 falls until equilibrium has been restored.If, when the pressure in the stopper 20 drops, the predetermined minimumpressure value is reached, a control signal is likewise sent to thecontroller 52 for the support elements 16 which, by way of a computer54, so alters the supporting forces that a state of equilibrium in theregion of the target pressure value is restored.

If the external disturbing forces acting upon the roll sleeve 14 are sogreat that it is not possible to compensate for them, there is a systemmalfunction. When the roll sleeve 14 moves upwards and the pressure inthe stopper 20 rises to a predeterminable upper limit, a control signalcauses a stack of rolls in a calender arrangement to open, indicating asystem malfunction. Correspondingly, when the roll sleeve 14 movesdownwards when there is a fall in pressure in the stopper 20 to apredeterminable lower limit, the stack of rolls is likewise opened(released), indicating a state of malfunction in the calenderarrangement.

To close a stack of rolls of a calender arrangement according to FIGS.14a and 14 b, in which the above-described deflection controlled roll isarranged as a lower end roll 62, the following takes place. Thevolumetric flow of the hydraulic oil is sent to the two secured,backward-facing stoppers 20. The pressure at that moment is virtuallyzero since the roll sleeve 14 bears down in the bearings and the securedstoppers 20 have no contact with the roll sleeve 14. In the next step, asupport piston pressure is activated at the hydrostatic support elements16 and the roll sleeve 14 is thus raised. When the secured stoppers 20make contact with the roll sleeve 14, backward-directed forces build upwhich prevent the roll sleeve 14 from rising further. The roll sleeve 14is in the preset operating position. After closure of the stack ofrolls, the roll sleeve 14 is clamped at that operating positionhydraulically as explained above, it being possible to set thesupporting forces of the support elements 16 according to thepredeterminable line forces in the nips.

According to FIGS. 1 to 4, the pump 42 accordingly delivers a constantthroughput, that is to say constant volume per unit of time, it beingpossible for the pump to be, for example, a gear pump or anotherpositive-displacement pump. In addition to those volumetric pressuresources, volumetric flow distributors may also be used

The pump 42 pumps against the pressure prevailing in the line 40 and isso configured that it can do so until a pressure determined by anoverpressure valve 46 has been reached. The pressure in the line 40 isdetected by means of a sensor 50, in this case a pressure sensor, and isrouted to the controller 52 for the pressures for determining thesupporting forces of the hydrostatic support elements 16.

Let it be assumed that the roll sleeve 14 has been completely lowered.This is shown, for example, in FIG. 14a, where the above-describeddeflection controlled roll forms a lower end roll 62 of a calender,above which roll there is arranged an intermediate roll 63. The niplying between the two rolls 62, 63 is open.

The counter-pressure P in the line 40 in that position of the rollsleeve 14 is virtually zero because the gap width S of the seal gap 34is very large and the hydraulic medium is recirculated by the pump 42.

If the support elements 16 are then acted upon by pressure medium, theyraise the roll sleeve 14 in order to exert forces on a web of materialpassing through a nip, as shown in FIG. 14b. The roll sleeve 14 thusdraws closer to the sealing member 22 of the stopper 20. The gap width Sdecreases, the pressure across the gap increases and a downward force isexerted on the roll sleeve 14. If the forces are in equilibrium, theroll sleeve 14 is in a position corresponding to a gap height S1 inwhich pressure P1 prevails in line 40. This is the case when a targetposition and the actual position coincide.

If the position of the roll sleeve 14 departs from its target position,for example in the direction of a narrower gap and a higher pressure,the controller for setting the supporting forces of the hydrostaticsupport elements 16 would normally intervene to restore the targetposition. In the context of the invention it is, however, permitted forthe actual position to depart from the target position between an upperlimit P2/S2 and a lower limit P3/S3 (see FIG. 4) without intervention onthe part of the controller. The result is that the stoppers 20 define a“pseudo-stop” which is so configured that it will, by damping, take upany impacts. Only if the pressure exceeds the value P2 or falls belowthe value P3 will the controller intervene and try to restore the rollsleeve 14 to its target position. If, however, the maximum pressure P4(predetermined by the pressure limiter 46) is reached, the calenderarrangement will switch itself off since the predetermined control rangeof the controller will have been exceeded. The same applies when thepressure falls below a pressure P5.

In a variant, over the pressure range P2 to P3 it is possible tointegrate, on the one hand, instances where the pressure falls belowpressure P1 and, on the other hand, instances where pressure P1 isexceeded, and to determine the quotient of the two integrals. Thatquotient signal then indicates to the controller the trend in the changeof position of the roll sleeve 14. In a further variant, the controllercan also permit instances where P2 is exceeded and instances where thepressure falls below P3, provided they do not last beyond apredetermined period of time. Account should be taken of the fact thatthe controller has to be in control of a large number of interconnectedcontrol circuits, which means that it needs time to evaluate any controlsignals. Even if, as is customary in calenders, a high-speed computer isused, the computer still requires a few tenths of a second of computingtime, whilst brief, possibly periodic disturbances may occur in the gap34 which are the result, for example, of unavoidable imbalances in theroll sleeves and/or intermediate rolls of a calender arrangement.

The geometry of the stoppers 20, especially the active diameter and thegap length, are variable within wide limits, with the result that it ispossible to set the pseudo-stop to be on the rigid side or on theyielding side. As already explained above, in principle a single stopper20 would suffice, but two are preferred because any tendency of the rollsleeve to become skewed can thus be detected and avoided.

As explained above, during operation the plunger 22 is in permanentcontact with the bolt heads 26, with the result that it could actuallybe fastened in a fixed position on the roll axle 10. Its ability to bedisplaced into the axle is a safety measure in order to avoid frictionalcontact between the roll sleeve 14 and the stopper 20 under anycircumstances.

Moreover, it is also possible to use quasi-volumetric or non-volumetricpressure sources. It is then important, however, that in the case of thenecessary maximum pressure that can prevail in the stopper 20, there isstill a minimum flow which safeguards the hydrostatic function for thatoperating state as well. Hydrostatic function means that mixed frictiondoes not occur between the end surface 32 of the sealing element 22 andthe internal wall 13 of the roll sleeve 14, and damage due to wear canbe reliably avoided at those sites.

FIG. 5a is a diagrammatic, partly sectional side view of a calenderarrangement according to the invention, in which the rolls are arrangedalong a vertical stack plane and where the upper end roll 60 is providedwith the positioning device. The lower end roll 62, however, also hasthe necessary built-in components so that all that is needed is toprovide a roll design that can be used either as an upper or lower endroll, yielding logistical advantages. Intermediate rolls 63 are arrangedbetween the upper end roll 60 and the lower end roll 62. Theintermediate rolls 63 are arranged to be movable vertically by means oflever mechanisms 64. The bearings of the lower end roll 62 are alsoadjustable vertically by means of a lifting device 65. The stoppers 20in the upper end roll 60 are arranged on the backward-facing side of theroll. The same applies to the lower end roll 62.

It is preferable for the roll sleeve of the lower end roll to bepositioned. The stoppers in the upper end roll then drop into the axleand have no contact with the internal wall of the roll sleeve.

According to FIG. 5b, the rolls 60, 62, 63 are arranged along an obliquestack plane. The intermediate rolls 63 are arranged to be movable in theoblique direction by means of lever mechanisms 64. The bearings of thelower end roll 62 are also adjustable oblique by means of lifting device65.

According to FIG. 5c, the rolls 60, 62, 63 are arranged along ahorizontal stack plane.

The intermediate rolls 63 are arranged to be horizontally movable bymeans of lever mechanisms 64. The bearings of the end roll 62 are alsoadjustable horizontal by means of a displacement device 65.

FIG. 6 shows a stop element that has been modified with respect to FIG.2; components having the same function have been given the samereference numerals as in FIG. 2. The screw bolts 28 from FIG. 2 are herereplaced by tappets 29, the axle-facing end of which carry a piston 31.Supplied with hydraulic medium via line 33 or line 35, the tappets canadopt an upper end position (as shown) or a lower end position, so thattwo different target positions of the roll sleeve can be selectedwithout having to take the roll apart. The pressures in the lines 33, 35and 37 must of course be in agreement with one another so that theplunger 22 is always held in the desired end position.

Another possibility for presetting different target positions of theroll sleeve is shown in FIGS. 7 and 8. Instead of the two stoppers 20from FIG. 1, two pairs of stoppers 70 are provided, the stoppers 70forming each pair having bolts 28 of different lengths. Only one stopperin each pair is acted upon by hydraulic medium, whereas the other has apressure-free connection. In FIG. 8 the stopper shown on the lefthandside is active. Further target positions for the roll sleeve can ofcourse also be preset by groups of three or even more stoppers.

Insofar as the above has taken as its reference only a vertical stack ofrolls, it relates only to the customary manner of calender construction.The invention could of course also be used if the plane defined by theroll axles had a different spatial orientation.

FIGS. 9 and 10 show a third embodiment of a suitable deflectioncontrolled roll in which a stopper 70 is provided with a holding bolt 28and forms a group with at least one hydrostatic support element 71without a holding bolt. In that variant the support element 71 without aholding bolt always rests against the internal circumference 13 by meansof a support piston pressure, that is to say even when the roll sleeve14 has moved away from the stopper 70. For that purpose the elements 70,71 are connected via lines 73, 74 to a common pressure supply linehaving a volumetric pressure source.

In the fourth embodiment according to FIGS. 11 and 12, in a group of aplurality of stoppers 70 all the stoppers are provided with holdingbolts 28 of the same length and are connected to a common volumetricpressure source. That configuration avoids the mentioned disadvantage ofthe third embodiment since, after the roll sleeve has moved away fromthe stopper 70, all the elements are limited in their stroke by theirholding bolts 28 and thus can not follow the movement of the roll sleevefurther. The functional operation of that solution is also safeguardedwhen the lengths of the holding bolts 28 have unavoidable tolerancedifferences. The operating position of the roll sleeve is thendetermined by the element 70 having the shortest holding bolt 28.

Finally, FIG. 13 shows a construction of a stopper 80 in the form of ahydrostatic support element having holding bolts 28 using a hydrostaticsupport plunger 81.

What is claimed is:
 1. A calender comprising: a frame; and a number ofrolls arranged in a stack on the frame; said stack defining a stackplane, in which the rolls are arranged to form nips including end rollsat opposite ends; wherein the end rolls each comprise: a roll axlenon-rotatingly secured to the frame; a roll sleeve received over theroll axle so that said roll sleeve can both rotate and move radially inthe direction of the nips relative to the roll axle; a plurality offirst hydrostatic support elements mounted on the roll axle, whichsupport elements can be displaced in the direction of the nips to movethe roll sleeve relative to the roll axle; and at least one stop elementmounted on the roll axle which acts on the roll sleeve in a directionopposite to that of the first hydrostatic support elements; wherein thestop element comprises; a second hydrostatic support element including apiston which is positioned in a cylinder bore and on which a pressureelement is applied to move the piston radially under force relative tothe roll axle; and a stop member to adjustable limit such radialmovement to a predetermined maximum displacement relative to the rollaxle to place a surface of the piston next to an inner surface of theroll sleeve by including a seal gap, and means for delivering a constantflow rate of a hydraulic medium into the cylinder bore, and the pistonhaving passages through which said fluid flows into and out of the sealgap.
 2. A calender as in claim 1, wherein the stack plane is vertical,oblique or horizontal.
 3. A calender as in claim 1, further comprising acontrol device connected to monitor the pressure of the hydraulic mediumflowing through the gap, wherein a decrease in the gap increases thepressure and a decrease in the gap increases the pressure.
 4. A calenderas in claim 1, wherein the rolls each include at least two stop elementsdisposed symmetrically with respect to the middle of the length of thesleeve.
 5. A calender as in claim 4, wherein the at least two stopelements are spaced inwardly from each end of the sleeve by one-quarterthe length of the sleeve.
 6. A calender as in claim 1, wherein the stopmember comprises at least one bold.
 7. A calender as in claim 6, whereinthe bolt includes a bolt head which is adjustably positionable relativeto the axle.
 8. A calender as in claim 7, further comprising means forhydraulically adjusting the position of the bolt head relative to theaxle.
 9. A calender as in claim 6, comprising a plurality of hydrostaticbearings each having at least two bolds having different lengths.
 10. Acalender as in claim 1, further comprising a pump and a supply linewhich connects an output of the pump to the hydrostatic supports.
 11. Acalender as in claim 10, wherein the pump comprises a positivedisplacement pump.
 12. A calender as in claim 11, further comprising apressure limiting valve in the supply line.
 13. A calender as in claim10, further comprising a pressure monitoring device connected to monitorpressure in the supply line and a control device connected to thepressure monitoring device.
 14. A calender as in claim 13, wherein thecontrol device adjusts a stroke of the internal sleeve whenever pressurein the supply line exceeds a predetermined upper or lower threshold. 15.A calender as in claim 10, wherein the means for delivering a constantflow rate of the hydraulic medium comprises the pump.
 16. A deflectioncontrolled roll for use with a calender for treating a product web, saidroll comprising: a non-rotating roll axle; a roll sleeve received overthe roll axle so that said roll sleeve can both rotate and move radiallyto the roll axle; and inside loading means disposed in at least one rowon the non-rotating axle for supporting the roll sleeve, said insideloading means for comprising; a plurality of first hydrostatic supportswhich are radially displaceable relative to the non-rotating roll axleto provide an internal roll sleeve stroke; at least one stop elementdisposed on a side of the non-rotating roll axle opposite to thehydrostatic supports, said element comprising: a second hydrostaticsupport element including a piston which is positioned in a cylinderbore and on which a pressure element is applied to move the pistonradially under force relative to the roll axle; and a stop member toadjustable limit such radial movement to a predetermined maximumdisplacement relative to the roll axle to place a surface of the pistonnext to an inner surface of the roll sleeve by including a seal gap, andmeans for delivering a constant flow rate of a hydraulic medium into thecylinder bore, and the piston having passages through which said fluidflows into and out of the seal gap.
 17. A deflection controlled roll asin claim 16, further comprising a device for measuring a change inpressure in the gap between a surface of the piston and an inner surfaceof the roll sleeve and a signal indicator connected to the pressurecharge measuring device which indicates radial position change of theroll based on a change in pressure.
 18. A deflection controlled roll asin claim 17, wherein the pressure change measuring device comprises apressure sensor which measures a pressure of the hydraulic medium.
 19. Adeflection controlled roll as in claim 17, further comprising a controldevice which controls the hydraulic medium delivering means in responseto the pressure measured by the pressure measuring device.
 20. Adeflection controlled roll as in claim 16, further comprising a pressurelimiting valve connected to the hydraulic medium delivering means tolimit a maximum pressure in the gap.
 21. A deflection controlled roll asin claim 16, further comprising a pump and a supply line which connectsan output of the pump to the hydrostatic supports.
 22. A deflectioncontrolled roll as in claim 21, wherein the pump comprises a positivedisplacement pump.
 23. A deflection controlled roll as in claim 21,wherein the hydrostatic supports comprise hydrostatic bearing pocketsconnected to the supply line.
 24. A deflection controlled roll as inclaim 23, further comprising a seal around the bearing pocket.
 25. Adeflection controlled roll as in claim 16, wherein the stop elementcomprises at least one bolt which is adjustably positionable relative tothe axle.
 26. A deflection controlled roll as in claim 16, including atleast two step elements disposed symmetrically with respect to themiddle of the length of the sleeve.
 27. A deflection controlled roll asin claim 26, wherein the at least two stop elements are spaced inwardlyfrom each side of the sleeve by one-quarter the length of the sleeve.28. A method for calendering a web, said method comprising: passing theweb through nips between rolls arranged in a stack along a stack plane,including deflection controlled end rolls and intermediate rolls betweensaid deflection controlled end rolls, delivering a pressure of force toat least one of said deflection controlled end rolls, being aself-loaded roll, to maintain a predetermined value of an internalstroke length, delivering a hydraulic medium at a constant flow rate tothat at least one deflection controlled end rolls, wherein the hydraulicmedium flows between a gap between a hydrostatic support element and aninner surface of the roll sleeve so that a radial movement of the rollsleeve narrowing the gap increases the pressure of the hydraulic mediumto keep the gap and movement of the roll sleeve enlarging the gapdecreases the pressure of the hydraulic medium to keep the gap.
 29. Amethod as in claim 28, further comprising measuring the pressure of thehydraulic fluid, comparing the measured pressure with a target pressure,and adjusting the position of the at least one upper and lowerdeflection controlled rolls based on a difference between the measuredand target pressures.